Bipolar cells in the salamander retina can be classified into two major types according as to whether they are hyperpolarized or depolarized by illumination of the center of their receptive field. In either case, illumination with an annulus of light results in a response of opposite polarity. This antagonistic effect of the surround, however, is seen only when the center is dark or dimly illuminated; when the center is brightly illuminated, flashing an annulus evokes no response. The circuitry underlying this interaction between center and surround is being studied at present.